The present invention relates generally to railway train sets, and more particularly, to a system and method for generating head end power for use in passenger train sets.
In many regions of the world, particularly in large cities, passenger rail is a widely used mode of transportation. In these regions, people often use passenger trains to commute to the workplace from suburbs or smaller towns outside the city. The passenger train makes frequent stops and passes through residential areas as well as travels in congested urban areas. A passenger train's travel through these areas is accompanied by high levels of noise and harmful emissions, which is undesirable both for the train's passengers and residents of the area.
Both freight trains and passenger trains generally include a locomotive having a primary power source (e.g., a main generator or alternator) driven by a diesel engine to provide traction power to drive the train's wheels. Both freight and passenger train locomotives also connect to one or more railcars. However, unlike freight railcars, passenger railcars require electrical power for various housekeeping applications unrelated to locomotion, such as heating, cooling, ambient lighting, and energizing electrical outlets. To provide energy to the railcars for these housekeeping applications, locomotives for passenger train sets also include a head end power (HEP) system.
To provide head end power, known HEP systems typically include either a parasitic generator driven by the main (traction) engine in addition to the primary power source or a separate smaller engine/generator set that operates independently of the main engine. Both types of HEP systems have their drawbacks. For instance, because the parasitic generator obtains its energy from the main diesel engine, less horsepower is available for accelerating the train and/or the engine has to maintain higher power output and fuel consumption to sustain the desired cruising speed. While a separate engine/generator set dedicated to non-propulsion purposes would not rob energy from the primary power generator, the use of a separate system translates into higher maintenance costs for the passenger train. In addition, both types of HEP systems produce undesirable levels of high-pitched noise as they utilize generators that run at high RPMs. This noise is particularly bothersome in passenger trains as it affects the comfort of the passengers, bystanders, and residents. Also, both types of systems require the consumption of additional fuel, which again translates into higher costs, as well as increased emission levels. In light of these drawbacks, it would be desirable to provide a low noise HEP system that requires less or even no extra fuel to operate and which does not detract from the primary power available for traction and acceleration.
One source of unused energy available on locomotives is energy generated from dynamic braking. When the train is in the motoring mode, the main engine rotates the primary power source that powers the traction motors which provides the tractive power to drive the train's wheels. When dynamic braking is activated, a dynamic braking control system reconfigures the traction motors as generators which are rotated by the forward momentum of the locomotive and the attached railcars, thus producing electrical energy. This action produces drag on the traction motors/generators and, thus, provides a braking effect. In traditional dynamic braking locomotives, the energy generated by the dynamic braking action is transferred to a resistor grid where it is converted to thermal energy and dissipated through the cooling effect of a fan system. In other words, the excess energy is wasted.
There have been attempts to make productive use of the excess energy generated by dynamic braking. For instance, freight applications have captured the excess energy and then used it to selectively supplement or replace the primary energy provided to the traction motors when in the motoring mode. However, as freight trains do not make frequent stops, dynamic braking in freight applications does not provide enough excess energy for an application where the demand for the energy is continuous. Other applications do not capture the excess energy at all, but instead immediately use the energy as it is generated.